login
A164634
Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.
0
1, 21, 420, 8400, 168000, 3360000, 67200000, 1343999790, 26879991600, 537599748210, 10751993288400, 215039832252000, 4300795974720000, 86015906088000000, 1720317853632043890, 34406351710082593500
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170740, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
FORMULA
G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^7 - 19*t^6 - 19*t^5 - 19*t^4 - 19*t^3 - 19*t^2 - 19*t + 1).
CROSSREFS
Sequence in context: A163145 A163503 A163977 * A164954 A165358 A165894
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved